Question: On the first 3 tests of her math class, Tiffany got an average score of 79. What does she need on the next test to have an overall average of 83?
Answer: Let her score on the next test be $x$ The sum of all of her scores is then $3 \cdot 79 + x$ The same sum must also be equal to $4 \cdot 83$ Solve: $x = 4 \cdot 83 - 3 \cdot 79 = 95$.